This invention relates generally to optical wavelength division multiplexing and, more particularly, to a technique for combining multiple signals of different wavelengths, on separate optical fibers, into a single beam for transmission along a single optical fiber or through space. The invention has application in high capacity laser communication systems.
Dispersive gratings and prisms have been used in the past for optical wavelength multiplexing, as have dichroic beam splitters, but the techniques of the prior art are either unsuitable for large numbers of input channels, or are grossly inefficient from an energy standpoint.
Typically, optical signals to be multiplexed are made available on separate optical fibers, from which light cannot be easily launched into a single fiber. Moreover, although the individual fibers are small, ends of closely spaced fibers nevertheless emit light from different spatial locations. Another difficulty is that the nominal wavelength of each laser source may drift in value as temperature and other parameters change with time. Any variation in the wavelengths adversely affects the alignment of optical components used for wavelength multiplexing when combined with a dispersive approach. Accordingly, there is still a need for an optical wavelength multiplexer capable of handling a relatively large number of inputs and reliably producing an output beam that is kept aligned by controlling drift in wavelength. The present invention satisfies these requirements.